Revealing Generality of the Thermodynamic Properties for Crystals of Long-Chain Aliphatics and Polymethylene

Abstract

We analyze the dependency of melting points of molecular crystals with different chain lengths on the crystal habit of elementary volume for the first-order phase transition. We demonstrate that molecular crystals with identical chemical structure of their cores—unbranched alkanes CH₃(CH₂)_nCH₃, diols HOC(CH₂)_nCOH, unbranched aliphatic alcohols CH₃(CH₂)_nCOH, saturated carboxylic acids CH₃(CH₂)_nCOOH, and dicarboxylic acids HOOC(CH₂)nCOOH—lose their identity and individual properties and evolve toward polyethylene as the number of repeating–CH₂–groups increases.